Recent events and discoveries have resulted in a major increase in activity in the development of electrical cars. However, although significant advances have been made in the technology of electric motors and motor controls which make electrical cars feasible, electrical cars cannot become a reality until devices and methods are provided for charging the batteries of such vehicles safely at home, at work, and in shopping districts. Since the energy requirements for charging stations for electric cars are very high, on the order of 100 amperes or more per vehicle, it is likely that a disruption of the power grid could occur if thousands of battery chargers began charging automotive batteries at the same time. This could readily occur after a power failure if the chargers were allowed to begin charging immediately upon the restoration of power, or early in the morning when workers all arrive at work simultaneously and begin charging their vehicles. Electrical utilities are therefore insisting that automotive chargers have manual reset mechanisms or some sort of device for insuring that the charger does not come on immediately upon the application of power.
From the user's point of view, manual reset mechanisms are unacceptable. A momentary power outage occurring while an automobile owner is sleeping or absent, or otherwise unable to reset the charger, could result in the charger not being reset, and the user could be faced with dead batteries when he returns to his car. To address this problem, it has been suggested that the reset mechanism be provided with an alarm to alert the owner to reset the charger. However, an alarm would be useless when the owner is not available to hear it, and it would be particularly objectionable if it went off during the middle of the night.
It has also been suggested that preset or user-selectable delays be provided to keep chargers from turning on for a certain period of time (e.g. 5, 10 or 15 minutes). However, preset delays would still allow a considerable number of cars to turn out at the same time. Furthermore, if users were permitted to select the duration of the preset, they would, most likely, select the shortest delay to give them the longest possible charge period. Also, a shopper may often run many errands at different locations, with each of the errands taking relatively short periods of time. The accumulated drain on the batteries might be such that the car needs to be recharged during the day at one of these locations. In this situation, a delay of 15 or 20 minutes might render the charge cycle too short to significantly affect the charge on the batteries.
Broadly, it is an object of the present invention to provide a method and apparatus for restoring power to battery chargers and other high current electrical devices, which method and apparatus eliminate the danger of a disruption of the power grid and also avoid the above-mentioned shortcomings. It is specifically contemplated that power should be restored to different electrical devices at different times.
It is another object of the present invention to provide a method and apparatus for restoring power to electrical devices following a power outage which do not depend upon a person to reset the power.
It is another object of the present invention to provide a method and apparatus for restoring power to electrical devices following a power outage which do not have preset turn-on delays or turn-on delays selectable by a user.
It is also an object of the present invention to provide a method and apparatus for restoring power to electrical devices subsequent to a power outage, which are reliable and convenient in use, yet relatively inexpensive in utilization or construction.
In accordance with the present invention, an automotive battery charger or other electrical device which draws substantial amounts of power is provided with a variable delay mechanism which prevents turn on of the device when power is applied. The duration of the delay is determined by a random or pseudorandom number generator, so that a plurality of different electrical devices will, in effect, be turned on at random times following application of power. The maximum turn on delay could be conveniently limited to a specific period of time, so that critical operating times of the device, such as the charging cycle of a battery charger, are not shortened excessively.